The invention relates to an apparatus for producing an expanded granulate from sand-grain-shaped material, comprising a furnace with a substantially vertically extending furnace shaft and a feed device arranged above or in the upper region of the furnace shaft for feeding the sand-grain-shaped material to the furnace shaft, wherein the feed device is formed to introduce the sand-grain-shaped material in form of at least one downwardly falling curtain into the upper region of the furnace shaft, wherein the drop section of the curtain lies in a decentralised, preferably peripheral region of the furnace shaft cross-section, and to a method for producing an expanded granulate.